Grinding mills for grinding crude ore generally comprise a rotatable cylindrical shell made of heavy steel plate and lined on the inside surface thereof with wear resistant shell liners. Lumps of ore are fed into one end of the mill and the ground product removed from the other end. Various types of mills utilize different kinds of grinding media, such as rods, tubes, and balls, to aid in the grinding. Other mills may use the autogeneous grinding method where the ore itself is employed as its own grinding media. In the semi-autogeneous mill, a mixture of ore and steel charge is used as the grinding medium.
The inner peripheral surface of the grinding mill is subjected to a great deal of wear and tear and therefore must be adapted to withstand the continuous impacts and abrasion of ore tumbling in the mill during grinding. To control the movement of the ore in the mill and to protect the steel shell against abrasion and erosion, wear resistant shell liners are mounted onto the inner peripheral surface.
Generally speaking, liner assemblies comprise a plurality of substantially flat liner members supported in cylindrical array by being individually bolted to the inner surface of the grinding mill shell. The liners may be alternately spaced by lift-bars for lifting the ore to the top of the rotating shell or drum from which the ore tumbles by gravity to the bottom where it is crushed or reduced to size by impact. On the other hand, the liners themselves may be configurated with raised rib portions to act as lifters in raising the ore. In semi-autogeneous grinding mills containing grinding media, the lift-bars or ribs similarly raise the grinding media which tumbles to the bottom of the shell and impacts against the ore.
As will be clearly apparent, shell liners are subjected to aggravated wear and tear due to continuous high impact loads and abrasion during the grinding operation, thus requiring periodic replacement of the liners.
As stated hereinbefore, in the grinding of ore large pieces of ore are fed at one end (the feed section) and discharged at the opposite end (the discharge section) in the desired reduced size. Thus, the wear and tear may be greatest during the portion of the grinding cycle where the large ore pieces move from the feed section immediate the end to the intermediate section of the mill. At the entrance end, not much grinding occurs, such that the liners at this end are not subject to the aggravated wear and tear as occur when the large pieces move to the end of the feed section adjacent to the intermediate grinding section of the mill (near the middle of the mill) where the mass lifting and tumbling of the large ore pieces subject the liners at this region of the mill to a great deal of wear. The smaller pieces or particles of ore approaching the discharge section do not provide the same impact against the liner, the reduction of the ore being due substantially to attrition. Thus, less wear occurs near the discharge portion of the mill.
Because of the foregoing mill grinding characteristics, liners of substantially uniform cross section are subjected to non-uniform wear which may require early replacement of worn liner parts and which may result in great scrap loss, especially where the liners are relatively thick along the whole length thereof.
Generally speaking, a shell liner is comprised of a plurality of metal segments (made, for example, of manganese steel) mounted in end-to-end relationship, with their flat ends almost touching, a small gap being generally provided between the ends. Because the liners are subject to great impact as described hereinabove, metal flow occurs along the length of the liner (linear strain), wherein the linear expansion of the liner segments creates great pressure at abutting flat end faces which tends to lock the liner segments in place and makes it difficult to remove them for maintenance purposes.
Examples of various types of shell liners are disclosed in the following U.S. Pat. Nos. 2,993,656; 3,107,867; 3,318,537; 3,582,007; 3,604,637; and 3,802,634.
U.S. Pat. No. 2,993,656, in particular, discloses liners comprised of a plurality of segments positioned in end-to-end relationship with a slight gap between adjacent flat end faces thereof. Such liner segments can lock in place due to linear strain along the length thereof, thus making it difficult to remove the liners for maintenance and repair.
It would be desirable to provide a segmented shell liner design that takes into account the linear strain produced during grinding operations such that the liner segment can be easily removed for shell maintenance purposes.